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| United States Patent |
5,734,867
|
|
Clanton
, et al.
|
March 31, 1998
|
Method, device, microprocessor and microprocessor memory for
instantaneous preemption of packet data
Abstract
The present invention provides a method (500), device (400), microprocessor
(500) and microprocessor memory (400, 500, 600) for instantaneous
preemption of packet-switched data from a user that has won contention for
a channel and for transmitting on a time slot, by higher priority traffic
type data or voice in a TDMA communication system having a central access
manager and a plurality of subscriber units. Before transmitting a packet
on an uplink channel, the subscriber unit first selects a time slot and
contends for channel access on the time slot. Upon gaining access to the
uplink channel, the subscriber unit begins transmitting segments of a data
packet on the selected time slot, suspending transmission when a higher
priority user gains access to the time slot and, where decoding fails,
suspending transmission for the time slot. The subscriber unit continues
to transmit on the selected time slot until the packet ends.
| Inventors:
|
Clanton; Christopher Lamonte (Chicago, IL);
Smolinske; Jeffrey Charles (Hoffman Estates, IL);
Tran; Phieu Moc (Lincolnwood, IL)
|
| Assignee:
|
Motorola, Inc. (Schaumburg, IL)
|
| Appl. No.:
|
508693 |
| Filed:
|
July 28, 1995 |
| Current U.S. Class: |
370/461; 370/337; 370/345; 370/458; 455/12.1 |
| Intern'l Class: |
H04M 003/56; H04J 003/16; H04Q 011/04; G06F 013/14 |
| Field of Search: |
395/500,860
370/431,458,459,345,444,461,462,348
340/825.03
455/34.1,12.1
|
References Cited
U.S. Patent Documents
| 4199661 | Apr., 1980 | White et al. | 370/461.
|
| 4319353 | Mar., 1982 | Alvarez et al. | 455/13.
|
| 4330857 | May., 1982 | Alvarez et al. | 455/12.
|
| 4346470 | Aug., 1982 | Alvarez et al. | 370/13.
|
| 4507781 | Mar., 1985 | Alvarez et al. | 370/345.
|
| 5197125 | Mar., 1993 | Engel et al. | 370/458.
|
| 5237570 | Aug., 1993 | Smolinske et al. | 370/458.
|
| 5528585 | Jun., 1996 | Cooley et al. | 370/461.
|
| 5561669 | Oct., 1996 | Lenney et al. | 370/444.
|
| 5570411 | Oct., 1996 | Sicher | 455/34.
|
| 5598575 | Jan., 1997 | Dent et al. | 395/800.
|
| 5636223 | Jun., 1997 | Reardon et al. | 370/459.
|
Primary Examiner: Teska; Kevin J.
Assistant Examiner: Walker; Tyrone V.
Attorney, Agent or Firm: Stockley; Darleen J.
Claims
We claim:
1. A microprocessor for providing instantaneous preemption of
packet-switched data from a subscriber unit that has won contention for a
channel and for transmitting on a time slot, by higher priority traffic
type data/voice in a TDMA communication system having a central access
manager and a plurality of subscriber units, comprising:
A) a channel type comparator, for receiving control information from a slow
channel of the current time slot and for determining a channel type of the
time slot, either packet or non-packet, wherein, where the channel type is
non-packet, the microprocessor sends a signal to disable the subscriber
unit's transmitter for the duration of the current time slot, and where
the channel type is packet, the microprocessor enables a busy/idle
determiner;
b) a busy/idle determiner, operably coupled to the channel type comparator,
for determining whether the time slot remains busy, wherein, where the
time slot is idle, the microprocessor sends a signal to disable the
subscriber unit's transmitter for the duration of the current time slot,
and where the time slot remains busy, the microprocessor enables a
priority comparator;
c) a priority comparator, operably coupled to the busy/idle determiner, for
comparing the priority of the subscriber unit with the priority which was
read from the slow channel, wherein, where the priority of the subscriber
unit is less than the priority that was read from the slow channel, the
microprocessor sends a signal to disable the subscriber unit's transmitter
for the duration of the current time slot, and where the priority of the
subscriber unit is greater than or equal to the priority which was read
from the slow channel, the microprocessor enable the subscriber unit's
transmitter.
2. The microprocessor of claim 1 wherein the state of the channel includes:
A) channel type indication, for indicating one of: packet and
circuit-switched data; and
B) a priority status for indicating a present priority level for a time
slot.
3. The microprocessor of claim 1 wherein for a packet channel type, a
busy-idle state is determined.
4. A device for providing instantaneous preemption of packet-switched data
from a subscriber unit that has won contention for a channel and for
transmitting on a time slot, by higher priority traffic type data/voice in
a TDMA communication system having a central access manager and a
plurality of subscriber units, comprising:
A) a channel type comparator, for receiving control information from a slow
channel of the current time slot and for determining a channel type of the
time slot, either packet or non-packet, wherein, where the channel type is
non-packet, sending a signal to disable the subscriber unit's transmitter
for the duration of the current time slot, and where the channel type is
packet, enabling a busy/idle determiner;
B) a busy/idle determiner, operably coupled to the channel type comparator,
for determining whether the time slot remains busy, wherein, where the
time slot is idle, sending a signal to disable the subscriber unit's
transmitter for the duration of the current time slot, and where the time
slot remains busy, enabling a priority comparator;
C) a priority comparator, operably coupled to the busy/idle determiner, for
comparing the priority of the subscriber unit with the priority which was
read from the slow channel, wherein, where the priority of the subscriber
unit is less than the priority that was read from the slow channel,
sending a signal to disable the subscriber unit's transmitter for the
duration of the current time slot, and where the priority of the
subscriber unit is greater than or equal to the priority which was read
from the slow channel, enabling the subscriber unit's transmitter.
5. The device of claim 4 wherein the state of the channel includes:
A) channel type indication, for indicating one of: packet and
circuit-switched data; and
B) a priority status for indicating a present priority level for a time
slot.
6. The device of claim 4 wherein for a packet channel type, a busy-idle
state is determined.
7. Computer software, embodied in a memory of a microprocessor, for
providing instantaneous preemption of packet-switched data from a
subscriber unit that has won contention for a channel and for transmitting
on a time slot, by higher priority traffic type data/voice in a TDMA
communication system having a central access manager and a plurality of
subscriber units, the computer program having steps comprising:
A) receiving control information from a slow channel of the current time
slot and determining a channel type of the time slot, either packet or
non-packet, wherein, where the channel type is non-packet, a signal is
sent to disable the subscriber unit's transmitter for the duration of the
current time slot, and where the channel type is packet, a busy/idle
determiner is enabled;
B) determining whether the time slot remains busy, wherein, where the time
slot is idle, a signal is sent to disable the subscriber unit's
transmitter for the duration of the current time slot, and where the time
slot remains busy, a priority comparator is enabled;
C) comparing a priority of the subscriber unit with a priority which was
read from the slow channel, wherein, where the priority of the subscriber
unit is less than the priority that was read from the slow channel, a
signal is sent to disable the subscriber unit's transmitter for the
duration of the current time slot, and where the priority of the
subscriber unit is greater than or equal to the priority which was read
from the slow channel, the subscriber unit's transmitter is enabled.
8. The computer software of claim 7 wherein the state of the channel
includes:
A) channel type indication, for indicating one of: packet and
circuit-switched data; and
B) a priority status for indicating a present priority level for a time
slot.
9. The computer software of claim 7 wherein for a packet channel type, a
busy-idle state is determined.
10. A method for providing instantaneous preemption of packet-switched data
from a subscriber unit that has won contention for a channel and for
transmitting on a time slot, by higher priority traffic type data or voice
in a TDMA communication system having a central access manager and a
plurality of subscriber units, comprising the steps of:
A) receiving control information from a slow channel of the current time
slot and determining a channel type of the time slot, either packet or
non-packet, wherein, where the channel type is non-packet, a signal is
sent to disable the subscriber unit's transmitter for the duration of the
current time slot, and where the channel type is packet, a busy/idle
determiner is enabled;
B) determining whether the time slot remains busy, wherein, where the time
slot is idle, a signal is sent to disable the subscriber unit's
transmitter for the duration of the current time slot, and where the time
slot remains busy, a priority comparator is enabled;
C) comparing a priority of the subscriber unit with a priority which was
read from the slow channel, wherein, where the priority of the subscriber
unit is less than the priority that was read from the slow channel, a
signal is sent to disable the subscriber unit's transmitter for the
duration of the current time slot, and where the priority of the
subscriber unit is greater than or equal to the priority which was read
from the slow channel, the subscriber unit's transmitter is enabled.
11. The method of claim 10 wherein the state of the channel includes:
A) channel type indication, for indicating one of: packet and
circuit-switched data; and
B) a priority status for indicating a present priority level for a time
slot.
12. The method of claim 10 wherein for a packet channel type, a busy-idle
state is determined.
Description
FIELD OF THE INVENTION
The present invention relates generally to access control in a
communication system, and more particularly, to packet data preemption in
a packet communication system.
BACKGROUND OF THE INVENTION
In time-division multiple access (TDMA) packet-switched communication
systems, data from many different subscriber units is typically divided
into units called packets and transmitted over a common channel. Each
packet may be divided to form segments. Each segment occupies a discrete
time slot of T seconds within a frame. A frame is made up of n time slots,
where n is a positive integer. Thus, subscriber units can communicate with
a central access manager on a basis of non-overlapping transmission
bursts. Since there is no overlap, a same pair of frequencies, one for
uplink and one for downlink, may be assigned to all subscriber units using
a same central access manager. Each time slot on the uplink typically
consists of a guard time, a small control field called the slow channel
(SC), and a user data field called the fast channel. Each time slot on the
downlink typically consists of a synchronization field, the slow channel,
and the fast channel.
In a TDMA communication system which supports circuit-switched traffic and
various types of packet-switched traffic, for example, user data packets
and packets used for acknowledgment purposes, there is a need for an
efficient method to allow circuit-switched users to send short messages
without requiring a dedicated control channel, and packet-switched users
to send high-priority short packets instantaneously without going through
a contention process.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a communications system with architecture consisting of
subscriber units communicating over the air to a radio port that has
wireline access via a radio port control unit.
FIG. 2 is a schematic showing an exemplary frame, slot, and slow channel
structure for a TDM A system in accordance with the present invention.
FIG. 3 shows a schematic representation of an uplink packet wherein
packet-switched data is momentarily preempted by higher priority traffic
type data in accordance with the present invention.
FIG. 4 is a block diagram of a device for providing instantaneous
preemption of packet-switched data by a subscriber unit in accordance with
the present invention in a TDMA communication system.
FIG. 5 shows a flow chart of one embodiment of steps of the method of the
present invention that provides instantaneous preemption of
packet-switched data from a subscriber unit that has won contention for a
channel and for transmitting on a time slot, by higher priority traffic
type data in a TDMA communication system having a central access manager
and a plurality of subscriber units.
FIG. 6 is a block diagram of one embodiment of a microprocessor for
providing, in accordance with the present invention, instantaneous
preemption of packet-switched data from a subscriber unit that has won
contention for a channel and for transmitting on a time slot, by higher
priority traffic type data or voice in a TDMA communication system having
a central access manager and a plurality of subscriber units.
DETAILED OF A PREFERRED EMBODIMENT
The present invention provides a method for instantaneous preemption of
packet-switched data from a subscriber unit that has won contention for a
channel and for transmitting on a time slot, by higher priority traffic
type data in a TDMA communication system having a central access manager
and a plurality of subscriber units. Before a subscriber unit may transmit
a packet on an uplink channel, the subscriber unit must first select a
time slot and contend for channel access on the selected time slot. Upon
successfully gaining access to the uplink channel, the subscriber unit
begins to transmit segments of a data packet on the selected time slot,
checking the channel state of the time slot before each transmission, and
suspending transmission whenever the subscriber unit fails to decode the
downlink or the channel state indicates that a user with a higher priority
has ownership of the time slot. When the channel state indicates that the
subscriber unit again has ownership of the time slot, the subscriber unit
continues to transmit on the time slot until the packet ends.
FIG. 1, numeral 100, depicts a communications system with architecture
consisting of subscriber units (102) communicating over the air to a radio
port (104) that has wireline access via a radio port control unit (106).
The radio port and the radio port control unit will be jointly referred to
as the central access manager (CAM) (108) in this document. The subscriber
unit may be a self-contained device capable of communicating directly over
the air to a CAM, or it may consist of a simple data terminal paired with
a second device that provides indirect communication with the CAM. The
transmission path from the subscriber units to the CAM is called the
uplink and the path from the CAM to the subscriber units is called the
downlink. Using the time-division multiple access (TDMA) transmission
technique, a single uplink/downlink channel pair can provide service to a
plurality of subscriber units.
FIG. 2, numeral 200, is a schematic showing an exemplary frame, slot, and
slow channel structure for a TDMA system in accordance with the present
invention. The TDMA technique is characterized by the duration of the time
frame and the duration of each time slot (202) within the time frame.
These factors generally depend on the system. In the figure shown, both
uplink and downlink channels consist of frames containing eight time slots
each. The time slots are numbered from 0 to 7. Uplink and downlink frames
are skewed such that a downlink frame, number K, occurs a fixed amount of
time (approximately nine time slots) before the uplink frame of the same
number occurs. The uplink time slot (206) that occurs approximately nine
slots after a given downlink time slot (204) is referred to as that
downlink time slot's corresponding uplink time slot. Similarly, the
downlink time slot that occurs approximately nine time slots before a
given uplink time slot will be referred to as that uplink time slot's
corresponding downlink time slot. A slow channel (SC)(208, 212) is a
portion of a time slot that contains control information. A fast channel
(FC) (210, 214) is a larger portion of a time slot that carries mostly
user data. The slow channel bit on a downlink time slot (204) indicates
the channel state of its corresponding uplink time slot (206). The channel
state includes a channel type and the priority level of the time slot.
FIG. 3, numeral 300, shows a schematic representation of an uplink packet
wherein packet-switched data is momentarily preempted by higher priority
traffic type data in accordance with the present invention. Subscriber
unit A, who has contended for and won access to the channel of time slot
0, decodes the downlink and reads the slow channel of time slot 0 in each
TDMA frame before transmitting on the corresponding uplink time slot of
the same numbered frame. Upon successfully reading the downlink slow
channel, subscriber unit A determines whether the channel state indicates
that subscriber unit A maintains ownership of the time slot. Where the
channel state indicates that subscriber unit A maintains ownership of the
time slot, e.g., T=0 and P=0, subscriber unit A transmits a segment of a
data packet (302). Where the channel state indicates that the current time
slot is reserved for higher priority traffic, a higher priority subscriber
unit, e.g., subscriber unit B with priority P=1, transmits data (304).
Then subscriber unit A, upon determining that the channel state indicates
that subscriber unit A has ownership of the time slot, transmits a new
segment of the data packet (306). Upon unsuccessfully decoding the
downlink time slot, subscriber unit A suspends transmission for the
duration of that time slot (308). This prevents subscriber unit A's data
from colliding with other data if the time slot happens to be reserved for
another subscriber unit. Then, upon determining that the channel state
indicates that subscriber unit A has ownership of the time slot,
subscriber unit A continues to transmit (310) a segment of the packet on
the time slot until determining that a higher priority subscriber unit has
ownership of the time slot. Then the higher priority subscriber unit,
e.g., subscriber unit C with priority P=2, transmits on the time slot
(312). For example, subscriber units B and C may be higher priority
packet-switched subscriber units (T=0 and P>0) which have received data
from the central access manager via the downlink fast channel and need to
transmit an acknowledgment to the central access manager or may be higher
priority circuit-switched subscriber units (T=1 and P.gtoreq.0) who need
to send control messages to the central access manager. Where ownership of
the time slot is again granted to subscriber unit A, subscriber unit A may
then continue to transmit on the time slot (314).
FIG. 4, numeral 400, is a block diagram of a device for providing, in
accordance with the present invention, instantaneous preemption of
packet-switched data from a subscriber unit that has won contention for
transmitting on a time slot, by higher priority traffic type data in a
TDMA communication system having a central access manager and a plurality
of subscriber units. The device (402) is typically coupled to a radio
frequency receiver and demodulator (408) of a TDMA communication system to
receive control information and includes: A) a logic gate (410), for
passing control information (slow channel) to the channel type determiner
if the decoding of the downlink time slot data is successful; B) a channel
type determiner (404), operably coupled to the logic gate, for utilizing
the control information for a time slot for determining a channel type of
the time slot; C) a priority determiner (406), operably coupled to the
channel type determiner, for one of: C1) allowing the subscriber unit to
transmit upon the subscriber unit's determining that the channel state
indicates that the subscriber unit maintains ownership of the time slot,
and C2) allowing a higher priority subscriber unit to transmit upon the
central access manage's assigning the time slot to the higher priority
subscriber unit, wherein, where the channel state is undecoded by the
subscriber unit, the subscriber unit fails to transmit data.
The channel state generally includes a channel type indication for
indicating packet or circuit-switched data and a priority status for
indicating a present priority level for a time slot. In general, for a
packet channel type, a busy-idle state is determined.
The device may be a microprocessor or, alternatively, the method of the
invention may be embodied in computer software, embodied in a memory of a
microprocessor, being a computer program loaded in the microprocessor for
providing instantaneous preemption of packet-switched data by a subscriber
unit that has won contention for a channel and for transmitting on a time
slot, by higher priority traffic type data in a TDMA communication system
having a central access manager and a plurality of subscriber units.
FIG. 5, numeral 500, shows a flow chart of one embodiment of steps of the
method of the present invention that provides instantaneous preemption of
packet-switched data by a subscriber unit that has won contention for a
channel and for transmitting on a time slot, by higher priority traffic
type data in a TDMA communication system having a central access manager
and a plurality of subscriber units. The method comprises the steps of: A)
determining, for each TDMA frame, a channel state of the time slot (502);
B) allowing the subscriber unit to transmit upon the subscriber unit's
determining that the channel state indicates that the subscriber unit
maintains ownership of the time slot (504); and C) allowing a higher
priority subscriber unit to transmit upon the central access manager's
assigning the time slot to the higher priority subscriber unit, wherein,
where a state of the channel is undecoded by the subscriber unit, the
subscriber unit fails to transmit data (506).
Typically, the channel state includes: A) channel type indication, for
indicating one of: packet and circuit-switched data; and B) a priority
status for indicating a present priority level for a time slot. For a
packet channel type, a busy-idle state is generally determined.
FIG. 6, numeral 600, is a block diagram of one embodiment of a
microprocessor for providing, in accordance with the present invention,
instantaneous preemption of packet-switched data from a subscriber unit
that has won contention for a channel and for transmitting on a time slot,
by higher priority traffic type data or voice in a TDMA communication
system having a central access manager and a plurality of subscriber
units. The microprocessor (608) includes a channel type comparator (602),
a busy/idle determiner (604), and a priority comparator. The channel type
comparator (602) receives control information from a slow channel of the
current time slot and is used to determine the channel type of the time
slot, either packet or non-packet. Where the channel type is non-packet,
the microprocessor sends a signal to disable the subscriber unit's
transmitter for the duration of the current time slot. Where the channel
type is packet, the microprocessor enables the busy/idle determiner (604).
The busy/idle determiner (604) is operably coupled to the channel type
comparator (602), and is used to determine whether the time slot remains
busy. Where the time slot is idle, the microprocessor sends a signal to
disable the subscriber unit's transmitter for the duration of the current
time slot. Where the time slot remains busy, the microprocessor enables
the priority comparator (606).
The priority comparator is operably coupled to the busy/idle determiner
(604), and is used to compare the priority of the subscriber unit to the
priority which was read from the slow channel. Where the priority of the
subscriber unit is less than the priority that was read from the slow
channel, the microprocessor sends a signal to disable the subscriber
unit's transmitter for the duration of the current time slot. Where the
priority of the subscriber unit is greater than or equal to the priority
which was read from the slow channel, the microprocessor enables the
subscriber unit's transmitter.
The present invention provides reliable and instantaneous preemption of
packets by a higher priority subscriber unit. Before transmitting on each
time slot, the subscriber unit must both decode the state of the selected
time slot and must determine whether transmission is allowed. If decoding
is unsuccessful or if transmission is prohibited, the subscriber unit
suspends transmission for the duration of that time slot.
Thus, the present invention requires that a current subscriber unit receive
verification that transmission is allowed for a selected time slot prior
to each transmission. Where a CAM determines that a higher priority user
requires use of a time slot selected by the current packet-switched
subscriber unit, the CAM may change the state of the time slot, Then the
current packet-switched subscriber unit immediately has access to the
change of state information and terminates the transmission on the time
slot. Thus, even where the current packet-switched subscriber unit
experiences channel failure, the current packet-switched subscriber unit
fails to receive access and thus does not transmit, allowing the higher
priority user to begin transmitting in spite of the failure.
In general, the invention allows a CAM to insert higher priority traffic
even before a current packet has been fully transmitted. That is, a
preemption may take place at any time slot boundary, rather than at a
packet boundary. This is accomplished by the CAM's changing the state of
the time slot for the duration of the higher priority packet, then
returning the time slot state to the previous state. The present invention
may be implemented in automatic repeat request schemes by assigning
retransmission packets to a different priority than regular data packets.
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